Random switch to 60hz refresh rate from 144hz.

I dont know why its doing it, and it seems to happen seemlessly. Whats weirder is that the control panel shows that the refresh rate is at 144hz, but it acts as if its at 60 for no apparent reason. The game I play can pick it up, and changing to a custom refresh rate above 60hz doesnt seem to actually produce the result, despite it saying that it has successfully done so. I assume its either a windows bug, or possibly the latest nvida driver 441.66.